The invention relates to a system for automatically and simultaneously loading a plurality of boat loads of semiconductor wafers into a semiconductor diffusion furnace.
Commonly assigned Pat. No. 5,765,982 by Martin et al., issued Jun. 16, 1998 is incorporated by reference herein, and is believed to be representative of the closest prior art. FIG. 1A of Pat. No. 5,765,982 shows a furnace loading station 10. A queue mechanism 30 having a stationary base is loaded with up to eight boatloads of semiconductor wafers 26. The queue mechanism 30 shifts the right hand boatload of wafers to an index position at the right end of queue mechanism 30 such that a pair of horizontal elevator tines 38 of a vertical elevator mechanism 34 can pick up one boatload of wafers at a time in the manner of a fork lift, raise them upward in the direction of arrows 60 into alignment with one of a number of horizontal loading assemblies such as 14 and 16. Each loading assembly includes a carriage such as 20 or 42 which moves horizontally on a track toward a semiconductor furnace tube located in a furnace cabinet on the right hand side of furnace loading station 10 so that up to eight boatloads of wafers supported on either a horizontal cantilever paddle such as 47 or in a horizontal cantilever diffusion tube such as 21 can be inserted into the hot zone of a corresponding furnace tube.
A horizontal robotic mechanism 37 is supported by vertical elevator 34. Horizontal robotic mechanism 37 supports the tines 38 which pick up one boatload of wafers and moves them horizontally in the direction of arrows 39 to position each boatload of wafers, one at a time, over the paddle 47, lower it onto the paddle 47. After up to eight boatloads of wafers have been loaded onto cantilever paddle 47, the carriage 42 supporting the paddle 47 moves in the direction of arrow 59 into the hot zone of the corresponding furnace tube. The entire operation is controlled by a programmed computer or control system 29 that controls the various described moving mechanisms.
A major shortcoming of the foregoing system of Pat. No. 5,765,982 is that the process of loading and unloading each cantilever paddle 47 with up to eight boatloads of wafers one at a time, inserting them all at once into and withdrawing them all at once from the furnace tube, the unloading of the processed boatloads of wafers, one at a time, and depositing them back on the queue mechanism 30 is very time-consuming. A typical prior art loading station 10 includes four loading assemblies such as 16, so 24 to 32 boatloads of wafers have to be transferred one at a time from queue mechanism 30 and loaded one at a time onto the cantilever paddles 47 prior to processing them in the furnace tube. After processing they then must be unloaded from paddles 47 one at a time and returned to queue mechanism 30. This may require a total of more than 15 minutes. The mechanism 30 in Pat. No. 5,765,982 is undesirably complex and slow.
Other prior art exists which provides an intermediate carrier that can support up to eight boatloads of wafers and load all up to eight boatloads in a single pass onto a cantilever paddle such as 47 in Pat. No. 5,765,982. Most such prior art systems use complex 5-axis articulated mechanisms to support the intermediate carrier and the up to eight boatloads of wafers on it. Both the hardware and software of these systems are more complex and expensive than is desirable. It is desirable that improvements to a wafer boat loading system occupy a minimum amount of space during operation and also be physically durable, in order to minimize amount of extremely expensive floor space required by a new wafer boat loading system in a new semiconductor fab unit, and to make the improvements easily retrofittable to an existing wafer boat loading system already installed in a wafer fab unit.
Accordingly, it is an object of the invention to provide an automatic wafer boat loading system which reduces the amount of time required to load a plurality of boatloads of semiconductor wafers into a semiconductor diffusion furnace and to later unload them from the furnace.
It is another object of the invention to provide an automatic wafer boat loading system which requires a minimum amount of space in which to operate.
It is another object of the invention to provide an improved automatic wafer boat loading system which includes a mechanically strong, stable boat handling apparatus and occupies a minimum amount of space during operation.
It is another object of the invention to provide an automatic wafer boat loading system which avoids the need for separate operations to load a plurality of wafer boats, one at a time, onto a cantilever paddle.
It is another object of the invention to provide an automatic wafer boat loading system which avoids generation of particulates due to abrasion that results from imprecise placement of loaded wafer boats on a cantilever paddle.
It is another object of the invention to provide an automatic wafer boat loading system which reduces the number of loading and unloading cycles required to load a plurality of boatloads of wafers into a diffusion furnace and later unload them from the furnace.
It is another object of the invention to provide an automatic wafer boat loading system which is operable using relatively simple software.
It is another object of the invention to provide a system for simultaneously loading a plurality of boatloads of wafers into a furnace tube while introducing a reduced amount of thermal mass and physical mass into the furnace tube so as to avoid disturbing semiconductor process parameters within the furnace tube by eliminating the need to use an intermediate carrier.
Briefly described, and in accordance with one embodiment thereof, the invention provides an apparatus for automatically and simultaneously loading a xe2x80x9clongxe2x80x9d wafer boat or a plurality of wafer boats onto a cantilever paddle, and automatically and/or simultaneously unloading the loaded wafer boats from the cantilever paddle. A stationary first track (16-1,43) is aligned with a first opening of a furnace, and a first carriage (42-1) is moveable on the first track, the first carriage (42-1) supporting the first cantilever paddle (47-1). The apparatus includes a first vertical translation mechanism (34A), a second vertical translation mechanism (34B), a first horizontal translation mechanism (50A) supported by the first vertical translation mechanism (34A), and a second horizontal translation mechanism (50B) supported by the first vertical translation mechanism. The first vertical translation mechanism (34A) includes a first stationary part (62A,63A) and a first vertically moveable support (61A), and the second vertical translation mechanism (62B,63B) includes a second stationary part (62B,63B) and a second vertically moveable support (61B). The first horizontal translation mechanism (50A) has a first base (86) supported by the first vertically moveable support (61A). The first horizontal translation mechanism includes a first horizontally moveable arm (51A) supported by the first base (86). The second horizontal translation mechanism has a second base supported by the second vertically moveable support, and includes a second horizontally moveable arm (51B) supported by the second base. A horizontal support apparatus (102) is adapted to support a plurality of wafer boats (24) each loaded with semiconductor wafers (26). The horizontal support apparatus (102) has a first end supported by the first horizontally moveable arm (51A) and a second end supported by the second horizontally moveable arm (51B). A stationary wafer boat edge lift member (97) has a first end rigidly supported by the first horizontally moveable arm (51A) and a second end rigidly supported by the second horizontally moveable arm (51B). A moveable wafer boat edge lift member (96) has a first end supported by and in moveable relationship to the first horizontally moveable arm (51A) and a second end supported by and in moveable relationship to the second horizontally moveable arm (51B). The moveable wafer boat edge lift member (96) includes first and second end portions supported by outer ends of first (97A) and second (97B) rotary arms, respectively, having inner end portions supported by first and second rotary drives supported by the first and second horizontally moveable arms, respectively. In the described embodiment, the first and second rotary drive mechanisms rotate the rotary arms to bring the moveable wafer boat edge lifting member (96) into a lower first position to engage an edge of a wafer boat (24) and to an upper second position above the wafers (26) in the wafer boat (24) so as to clear the wafers (26) as the first (50A) and second (50B) horizontal translation mechanisms are withdrawn from the wafer boat after they are set on the cantilever paddle.